Open Access
Add to BibSonomy
Abstract
Metasurfaces have demonstrated remarkable capabilities in manipulating light fields across diverse applications. However, current research tends to examine these functionalities in isolation, prompting a growing interest in integrating different functionalities within a singular metasurface device. In this paper, we propose and experimentally demonstrate a bifunctional metasurface capable of providing concealment and sensing functions simultaneously. Specifically, the proposed nanostructure effectively operates as a one-way mirror, exhibiting an average reflection rate of approximately 90% under external illumination, alongside an absorption rate of 87.9% from the opposite direction of incidence. This functionality renders it suitable for privacy-enhancing building windows. Meanwhile, this nanostructure also integrates liquid sensing capabilities boasting a sensitivity of 464 nm/RIU, which is particularly valuable for monitoring liquid-based corrosion. The experimental performance of the prepared 6-inch nanohole-patterned metasurface closely aligns with the simulations, and the utilization of flexible polyethylene terephthalate (PET) film, coupled with nanoimprint lithography technology, enables a direct and cost-effective manufacturing process that can be scaled up for widespread applications.
© 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Metasurface has been receiving great attention because of its unique characteristics of controlling the amplitude, phase and polarization of electromagnetic waves [1–5]. Due to their ultra-thin thickness, low losses, and ease of manufacture, metasurfaces have shown practical applications from visible to terahertz light, such as invisibility cloaks [6,7], light filters [8,9], scatters [10], reflectors [11] and negative-index metamaterials [12]. Apart from the typical single function, achieving multiple diverse functionalities in a single flat device is crucial for electromagnetic (EM) integration, and recent studies focusing on multifunctional metasurfaces have attracted considerable interest for their outstanding performance in device miniaturization and system integration. Given that amplitude stands as a fundamental parameter in the electromagnetic field of a light wave, the precise manipulation of incident light wave amplitudes at micro and nano scales holds significant scientific and practical importance. Presently, in the realm of amplitude modulation for metasurfaces, the majority of effort is geared towards extending bandwidth [13,14], reducing bandwidth [15,16], Fano resonance generation [17–19], and enhancing absorption or transmission efficiency [20–27]. Integrating multiple functionalities into a single metasurface device is still highly anticipated for diversified application scenarios. M. Liu et al. [28] introduced a versatile transmission mode utilizing an all-dielectric metasurface platform. This platform independently controls the phase and amplitude for two orthogonal states of polarization within the visible frequency range. Such advancements pave the way for developing compact multifunctional optical devices applicable in various fields such as polarization optics, information encoding, and security. C. Huang et al. [29] proposed a reconfigurable multifunctional metasurface with the capability to dynamically modify its local phase distribution, thereby achieving beam splitting across tunable frequency bands and predetermined electromagnetic response. The method demonstrated by this study provides functionalities aimed at mitigating backward scattering and enabling efficient polarization conversion. However, it is noteworthy that in the fabrication process, most studies heavily rely on electron beam lithography (EBL) or focused ion beam (FIB) milling [30–32]. This dependence restricts their applicability for large-area and mass production, primarily due to the time and cost involved in these methods.
Among the diverse research domains within metasurfaces, metasurface sensing has also garnered significant attention, particularly in the context of biomedicine and environmental monitoring, where surface plasmon resonance (SPR) sensors play a crucial role. Y. Wang et al. reported an SPR superstructure employing carbon nanotubes and optimized sensor performance using Fano model for detecting pesticide concentrations [33]. E. Ekmekci and G. T. Sayan reported a multifunctional sensor based on metamaterials capable of temperature, humidity, and density sensing by manipulating the dielectric constant and thickness of the interlayer medium [34]. In 2019, S. Agarwal and Y. K. Prajapati proposed a metasurface applicable for absorption and sensing in the 100-550 nm range [35]. This metasurface facilitated the detection of sucrose solution concentration with moderate accuracy and sensitivity, representing a notable instance of a multifunctional metasurface with a relatively simple nanostructure. To date, significant research efforts have also been dedicated to exploring programmable metasurfaces in the microwave and terahertz frequency domains, particularly for sensing, encryption, and detection [36,37]. These investigations light up the way for smart metasurfaces in fields such as artificial intelligence-assisted imaging displays and wireless communications.
In this paper, we present and experimentally demonstrate a bifunctional metasurface that integrates the concealing and sensing functions based on nanoimprinting. On one hand, the metasurface greatly reflects the warm-colored light, effectively achieving concealment by reflecting 92% of incident light and functioning as a one-way mirror. On the other hand, the metasurface exhibits high-quality SPR sensing characteristics with the sensitivity of 464 nm/RIU. Experimental findings are closely aligned with simulation results, validating the reliability of our approach. The fabrication process utilizes a 6-inch flexible PET substrate and incorporates nanoimprinting technology, offering the potential of cost-effective, simple, and scalable large-scale production. Besides, our bifunctional metasurface enables integration with glass, showcasing remarkable potential in applications such as smart windows or smart optical concealing systems. These applications extend beyond optical amplitude regulation and hold promise for diverse fields such as chemistry [38], biology [39,40], and environmental detection [41,42].
2. Design and simulations
One noteworthy application of our proposed bifunctional metasurface is its utility in smart windows, as illustrated in Fig. 1. The bifunctional optical metasurface is composed of periodic nanohole arrays and has a PET substrate. PET offers well transparency, allowing for minimal filtering of visible light. Additionally, its flexibility renders it suitable for application on both flat and curved surfaces, thereby expanding its versatility across various scenarios. When illuminated externally, the metasurface works as a reciprocal mirror that appears reflective on the patterned side and visible at the other. Consequently, this design prevents visibility from the exterior while allowing for internal viewing. Capitalizing on its narrow-band absorption spectrum, the metasurface is also adept at environmental monitoring, such as detecting acid rain. Fig. 1(b) and 1(c) display the top and sectional views of the nanostructure. The nanohole array, which is stamped onto the curable resist (PAP100, Diaotuo Tech, Shenzhen) film, features a cell period (P) of 500 nm in both the x and y directions. It has a diameter (D) of 250 nm and a depth (L) of 200 nm. Different metal layers are then deposited on the PET nanohole array, including a 5 nm chromium (Cr) layer (h1), an 80 nm silica dielectric spacer (h2), and a 100 nm top copper (Cu) layer (h3). Chromium serves as a prevalent adhesion layer material in metasurface fabrication processes. In the case of large-scale production, copper presents a more cost-effective alternative to gold and silver, thus enhancing economic viability. In the context of geometric optimization, a period of 500 nm holds promise for achieving a working bandwidth spanning both the visible and near-infrared spectra. This is owing to the fact that the resonant wavelengths of a periodic nanostructure tend to be approximately proportional to the period of the device. The optimization of diameter is intricately linked to practical fabrication considerations. Considering the deposition of an additional three-layer material, the diameter should exceed 200 nm to achieve adequate coverage while maintaining acceptable concealing performance. Furthermore, the thickness of each layer is fine-tuned to induce various resonance modes, thereby facilitating optimal intensity and bandwidth of the nanostructure. All simulations employ the three-dimensional (3D) finite-difference time-domain (FDTD) method. During simulation, “Periodicity” boundary conditions are applied in the x and y directions, while the z direction employs the perfectly matched layer (PML). Optical dielectric constants for Cu, SiO2 and Cr are obtained from Palik [43]. The refractive index of PAP100 is set as 1.56.
Fig. 1. (a) Schematic diagram of the bifunctional metasurface. (b) Stereoscopic view of the bifunctional cell with P = 500 nm, D = 250 nm. (c) The sectional view of the unit cell with h1 = 5 nm, h2 = 80 nm, h3 = 100 nm and L = 200 nm.
2.1 Bifunctional metasurface for optical concealing
We conduct a comprehensive analysis of the amplitude manipulation property of the bifunctional metasurface, considering perspectives from both the top and bottom of the structure. These perspectives correspond to external and internal viewpoints when the metasurface is affixed to a window or another object surface. In the scenario where light is incident from the outside, it initially illuminates the copper nanohole array, stimulating a strong localized SPP resonance. This intense resonance results in a dual-band reflection spanning from 690 nm to 810 nm and 855 nm to 1000 nm in the visible and near-infrared bands, as illustrated in Fig. 2(a). The calculated average reflection for these two spectral bands is 89.3%, with the highest reflection reaching 91.8% at 761 nm. Fig. 2(b) and 2(c) show the distribution of the electromagnetic field at 761 nm. It can be observed that the majority of the light is reflected into the air, indicating the metasurface's capability to obstruct visibility from the exterior and effectively execute optical concealing. Fig. 2(d) and 2(e) depict spectral reflectance comparisons under transverse electric (TE) and transverse magnetic (TM) polarizations at varying angles. It can be observed that in both modes, the metasurface exhibits high reflectance across the longer wavelength range at various angles, indicating that our structure can effectively reflect the warm-colored light and achieve optical concealing functionality across different angles.
Fig. 2. (a) Simulated reflection spectrum on the patterned side of the metasurface. (b) Electric field distribution and (c) magnetic field distribution of metasurface nanohole side in XZ direction. (d)-(e) Spectral reflectance under TE and TM polarizations at different angles.
On the contrary, the metasurface shows obvious broadband absorption from the interior viewing. Fig. 3(a) shows the light incident from the inside of the metasurface within the wavelength range of 300-1000 nm. The average absorptivity calculated in the wavelength range of 341-821 nm is 92%. Fig. 3(b) and 3(c) illustrate the distribution of electric and magnetic fields at a wavelength of 623.5 nm when TE-polarized light is incident perpendicularly to the bottom of the metasurface. In Fig. 3(b), it is evident that the surface plasma polariton (SPP) mode is excited within the metasurface structure. The electric field exhibits strength at the periphery of the nanoholes copper cylinder, facilitating the coupling of light to the adjacent nanoholes units, thereby generating SPPs and inducing light absorption. Fig. 3(c) reveal that at the wavelength of 623.5 nm, the robust magnetic field resulting from SPP resonance is confined primarily to the junction of Cu and SiO2. This resonance between the copper film on the surface and the SiO2 dielectric layer is attributed to propagating surface plasma resonance (PSPR). The resonance originating from the copper and chromium components within the nanohole corresponds to local surface plasmon resonance (LSPR). Consequently, the magnetic field is predominantly localized at the edges of the copper cylinder and the surface of the copper film within the nanohole. On the other hand, incident light traverses a 5 nm chromium layer and undergoes reflection at the interface between silica and the copper film. The interplay of the chromium layer with silica and the copper layer with silica forms a Fabry-Pérot (FP) cavity, resulting in a broadband absorption driven by FP resonance. Therefore, the field distribution at 623.5 nm indicates the resonance coupling of LSPR, PSPR, and FP resonances. To assess its performance under varying incidence angles, the impacts of TE and TM polarizations on absorption performance at different incident angles are depicted in Fig. 3(d) and 3(e). In both operational modes, the average absorption exceeds 80% within an angular range of 60° spanning from 300 nm to 800 nm. The aforementioned findings collectively suggest that our metasurface exhibits an optical concealing function—specifically, it prevents visibility from the outside while allowing partial visibility from the inside.
Fig. 3. (a) Simulated absorption spectrum of the bifunctional metasurface as light is incident from the PET side. Electric field distribution (b) and magnetic field distribution (c) in XZ direction. (d)-(e) The absorption spectra of TE and TM polarization at different incident angles.
2.2 Bifunctional metasurface for sensing
In addition, according to Fig. 2(a), the dual-band reflection simultaneously results in a narrowband absorption with a bandwidth of 53 nm, which in turn enables the sensing capability. To investigate the sensing performance of the metasurface, we recorded the reflection spectra in Fig. 4(a) for four different background refractive indices (n) of 1.333, 1.361, 1.376, and 1.431, corresponding to the solutions of deionized water, ethanol, isopropanol and glycol. As the refractive index of the ambient background increases, the reflection spectra produce a significant redshift, resulting in the respective resonant wavelengths of λ(n = 1.333) = 754 nm, λ(n = 1.361) = 767 nm, λ(n = 1.376) = 774 nm, and λ(n = 1.431) = 794 nm. The sensitivity (S) is then calculated by S=Δλ/Δn, where Δλ denotes the wavelength shift and Δn is the difference of refractive indices. Fig. 4(b) depicts the linear fitting results for sensitivity, which shows that the device achieves a sensitivity up to 401 nm/RIU. Taking the deionized water (n = 1.333) as an example, examining the electromagnetic field distribution at resonance wavelength 754 nm in Fig. 4(c) and 4(d), it is evident that the electric field concentrates above the nanohole, while the magnetic field is confined at the edge of the nanohole. This distribution feature in turn demonstrates that the localized surface plasmon resonance (LSPR) generated by the nanohole array is highly responsive to the external environment, contributing to its sensitive sensing performance. It is essential to highlight that the sample reagents used in our study are primarily for proof-of-concept purposes. Nevertheless, the results strongly suggest that the proposed metasurface exhibits significant potential for applications in smart windows designed for environmental monitoring. This includes scenarios such as assessing acid rain [44], alkaline rain [45], pesticide spray, and other related applications.
Fig. 4. (a) Simulated reflection spectra of the bifunctional metasurface with different types of solutions. (b) Linear fitting of refractive index sensitivity of simulated reflection spectra. (c) Electric field and (d) magnetic field distributions of the nanohole at 754 nm with a background refractive index n = 1.333.
3. Fabrication process
Figure 5 illustrates the fabrication flow chart of the bifunctional metasurface, which generally includes nanoimprinting (steps a-c) and electron beam evaporation (steps d-e). Initially, the nanostructure features from the silicon mode are imprinted onto the transparent polymer substrate through ultraviolet nanoimprint lithography (step a, UV-NIL, DT-R210, Diaotuo Tech, Shenzhen, China). The nanoimprint is done with a pressure of 0.6 Mpa, specifically chosen for its compatibility with brittle templates such as silicon or silica. Excessive or uneven pressure risks deformation, compromising pattern replication quality or even precipitating template fracture. The temperature is maintained at 25°C to eliminate errors stemming from variations in thermal expansion coefficients, curtailing heating and cooling durations and thereby enhancing operational efficiency. UV exposure time is set at 60 seconds utilizing a UV LED emitting at a wavelength of 385 nm. Inadequate exposure may induce deformation or detachment of the imprinting resist during demolding, impacting the template's lifespan, while an extended exposure may trigger material expansion, impeding demolding and potentially leading to structural cracking. The resulting cylinder array possesses a periodicity of 500 nm, a diameter of 250 nm, and a depth of 200 nm. Following this, a curable resist PAP100 is spin-coated onto a 125 µm thick PET substrate (step b). In the experiment, we use a 6-inch wafer as the substrate. In step (c), the coated substrate is stamped with the prepared complementary pattern template and exposed to UV irradiation. Subsequently, electron beam evaporation technology is employed to deposit a 5 nm Cr layer, 80 nm SiO2 layer and a 100 nm Cu layer onto the substrate (steps d-e).
4. Experimental results and discussion
4.1 Performance of optical concealing
Figure 6(a) depicts the scanning electron microscope (SEM, GeminiSEM 560, Zeiss) image of the imprinted sample, where the nanoholes are nearly uniform and measured approximately 200 nm. The reflective spectrum is investigated based on the commercial reflection spectrum measurement system (R3, Ideaoptics, China) depicted in Fig. 6(b). The halogen light source (HL2000, Ideaoptics, China) with a bandwidth of 300-2500 nm transmits through a 7-core Y-shaped fiber, of which six fibers in one branch work as the input channel. The light is then incident normally on the sample and reflects to the central fiber in the 7-core Y-shaped fiber. The central fiber functions as the receiving channel, directing the reflective light to the UV-visible-NIR spectrometer (PG2000-pro, Ideaoptics, China). The reflection spectrum is acquired using a gold mirror as a reference. Fig. 6(c) compares the simulated and experimental reflection spectra under an air background. The experimental results agree well with the simulations. The experimental reflection spectra exhibit an average reflectance more than 90% in two high-reflection bands, higher than the simulated results. As shown in Fig. 6(d), we produce a 6-inch sample by experiment, and take external photos of the sample outdoors. It can be seen that the mirror effect of the sample is excellent. Furthermore, as depicted in Fig. 6(e), due to the use of PET substrate, the sample exhibits notable flexibility that it retains its mirror-like properties even after undergoing bending. Moreover, in Fig. 6(f), images of the sample taken at angles of 0°, ± 30°, and ±60° reveal a consistently high-quality specular reflection across the sample surface, free from diffraction-induced rainbow glares.
Fig. 6. (a) The SEM image of the bifunctional metasurface sample featuring with nanohole. (b) Experimental setup for measuring absorption and reflection performance. (c) Comparison of the simulated and measured reflection spectra performance. (d) The exterior viewing of the metasurface sample taken from outdoors. (e) Sample flexibility test. (f) The optical images of the fabricated 6-inch sample taken at different light incidence of 0°, ± 30° and ±60°.
When light incidents from the unpatterned side, considered as the indoor environment, the metamaterial absorbs the majority of the incident light and allows a small portion to pass through, as illustrated in Fig. 7(a). The respective average absorption rate is measured as 87.9%. Consequently, it is clear seeing from Fig. 7(b) that the film exhibits a dark gray appearance and translucency.
Fig. 7. (a) Comparison of simulation and test results of metasurface absorption performance. (b) The interior viewing of the metasurface.
4.2 Performance of sensing
To ensure compatibility with the fabricated device, which features a nanohole diameter of 200 nm after the deposition of three-layer metals, we re-simulate the reflection spectra and its sensing performance under different background refractive indices, as shown in Fig. 8(a) and 8(b). In the sensing experiment, we use four different kinds of reagents as mentioned above, including deionized water (n = 1.333), ethanol (n = 1.361), isopropanol (n = 1.376), and glycol (n = 1.431). After each reagent change, the sample undergoes a thorough wash with isopropanol and deionized water, followed by air drying. The measured reflection spectra under different reagents are shown in Fig. 8(c). According to the four different reagents, the corresponding resonant wavelengths are measured as λ(n = 1.333) = 721 nm, λ(n = 1.361) = 733 nm, λ(n = 1.376) = 741 nm, and λ(n = 1.431) = 766 nm. As previously discussed, the resonance wavelength notably redshifts within 720-780 nm, aligning closely with the simulation results. The evaluated sensitivity based on the measured spectra reaches 464 nm/RIU, outperforming the simulation. Moreover, the wavelength difference between measurement and simulation remains under 3 nm. Given that a substantial and consistent wavelength shift holds greater importance than resonance intensity for a sensor, our proposed method effectively achieves high quality sensing.
Fig. 8. (a) Simulated reflection spectra with different background refractive indices. (b) Linear fitting of refractive index sensitivity of simulation reflection spectra. (c) Measured reflection spectra under different liquid backgrounds. (e) Linear fitting of refractive index sensitivity of experiment reflection spectra.
In order to provide a more precise assessment of the measurements, we employ the normalized mean square error (NMSE) to quantify the disparity between simulation and experimental outcomes. The NMSE is formally defined in Eq. (1), where n denotes the total number of samples, and IE and IT represent the experimental and simulated spectral data, respectively. As depicted in Table 1, all NMSE values fall below 9.7%, indicating a favorable concordance between the measurements and simulations. In particular, while the NMSE of spectral intensity for deionized water is slightly higher than that of other reference group, the discrepancy in measured resonance compared to simulated resonance remains below 3 nm, which is a critical consideration for sensing applications. Further investigation into the impact of deposited multi-layer materials on nanohole diameter and sidewall thickness during the fabrication holds promise for further error reduction.
Table 1. Error analysis between experiment and simulation based on NMSE method
4.3 Discussion
For the large-area samples produced, we conducted flexibility tests, specifically by bending the metasurface over cylindrical surfaces of large radii as shown in Fig. 6(e). The absorptivity and reflectivity performance of the designed structures remained essentially unchanged. This demonstrates that our device exhibits excellent optical and mechanical stability when used on smart windows. Moreover, PET has a heat resistance exceeding 70 °C, and the nanoimprint curable resist maintains a heat resistance surpassing 200 °C after UV curing. Therefore, in smart window application scenarios, the heat resistance and strong light resistance of the device are sufficient. A humid environment may accelerate the oxidation of the surface metal of the nanostructure, but substituting the surface metal with other corrosion-resistant metals, such as gold, can greatly mitigate this issue. Benefiting from the significant advantages of nanoimprint technology in large-area and low-cost fabrication, the large-area and flexible bifunctional metasurface proposed in this work holds immense potential for diverse practical applications in our daily life and optical precision instrument system. A prime example of its potential utility lies in smart windows, where the film allows internal viewing while deterring external observation., striking a balance between permitting natural light and providing privacy protection. Furthermore, its adaptability extends to applications in buildings, vehicles or optical precision instrument systems, where it can effectively enhance reflection, reduce heat and block harmful ultraviolet radiation. This not only contributes to energy conservation but also safeguards indoor items and optical precision instruments. Meanwhile, the sensing properties are particularly valuable for monitoring acid rain, alkaline rain or other corrosive substances, playing a crucial role in protecting buildings from liquid-based corrosion. This design presents a meaningful option in the exploration and application of multifunctional metamaterials, with anticipated widespread use in various fields in the future.
5. Conclusion
In summary, this paper introduces and experimentally demonstrates a large-area and flexible bifunctional nanohole metasurface operating in the visible light as well as near-infrared band. Utilizing soft nanoimprinting lithography, this metasurface integrates both optical concealing and sensing functionalities in a 6-inch PET substrate. In terms of optical concealing, the metasurface exhibits a wideband reflection with an average reflection rate of about 90% under external illumination, coupled with an 87.9% absorption from the opposite incidence direction. This particular amplitude regulation property is attributed to a combination of localized and propagating surface plasmon resonances, enabling internal viewing while inhibiting external observation. Regarding sensing performance, the measured sensitivity reaches to 464 nm/RIU associated with intensive LSPR. Our proposed nanostructure, which is highly feasible for low-cost mass-production, holds significant application potential in areas concerning smart windows, heat and radiation management, optical precision instrument protection, environmental monitoring and more.
Funding
Natural Science Foundation of Guangdong Province (2024A1515011802).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but maybe obtained from the authors upon reasonable request.
References
1. L. Bao, Q. Ma, G. D. Bai, et al., “Design of digital coding metasurfaces with independent controls of phase and amplitude responses,” Appl. Phys. Lett. 113(6), 063–502 (2018). [CrossRef]
2. S. Li, G. Wang, X. Li, et al., “All-dielectric metasurface for complete phase and amplitude control based on Pancharatnam–Berry phase and Fabry–Pérot resonance,” Appl. Phys. Lett. 11(10), 105201 (2018). [CrossRef]
3. H. P. Li, G. M. Wang, T. Cai, et al., “Phase-and amplitude-control metasurfaces for antenna main-lobe and sidelobe manipulations,” IEEE Trans. Antenn. Propag. 66(10), 5121–5129 (2018). [CrossRef]
4. L. Bao, X. Fu, R. Y. Wu, et al., “Full-space manipulations of electromagnetic wavefronts at two frequencies by encoding both amplitude and phase of metasurface,” Adv. Mater. Technol. 6(4), 2001032 (2021). [CrossRef]
5. T. Liu, X. Fu, J. Wang, et al., “Single-layer achiral metasurface with independent amplitude–phase control for both left-handed and right-handed circular polarizations,” ACS Appl. Mater. Interfaces 14(29), 33968–33975 (2022). [CrossRef]
6. H. Chu, Q. Li, B. Liu, et al., “A hybrid invisibility cloak based on integration of transparent metasurfaces and zero-index materials,” Light: Sci. Appl. 7(1), 50 (2018). [CrossRef]
7. X. Jing, D. Feng, Y. Tian, et al., “Design of two invisibility cloaks using transmissive and reflective metamaterial-based multilayer frame microstructures,” Opt. Express 28(24), 35528–35539 (2020). [CrossRef]
8. A. Ghobadi, H. Hajian, M. Gokbayrak, et al., “Bismuth-based metamaterials, from narrowband reflective color filter to extremely broadband near perfect absorber,” Nanophotonics 8(5), 823–832 (2019). [CrossRef]
9. Z. Liu, L. Qi, S. M. A. Shah, et al., “Design of broad stopband filters based on multilayer electromagnetically induced transparency metamaterial structures,” Materials 12(6), 841 (2019). [CrossRef]
10. L. Li, R. Lv, A. Cai, et al., “Low-frequency vibration suppression of a multi-layered elastic metamaterial shaft with discretized scatters,” J. Phys. D: Appl. Phys. 52(5), 055105 (2019). [CrossRef]
11. P. Moitra, B. A. Slovick, W. Li, et al., “Large-scale all-dielectric metamaterial perfect reflectors,” ACS Photonics 2(6), 692–698 (2015). [CrossRef]
12. M. Sadatgol, Ş. K. Özdemir, L. Yang, et al., “Plasmon injection to compensate and control losses in negative index metamaterials,” Phys. Rev. Lett. 115(3), 035502 (2015). [CrossRef]
13. M. Li, G. Wang, Y. Gao, et al., “An infrared ultra-broadband absorber based on MIM structure,” Nanomaterials 12(19), 3477 (2022). [CrossRef]
14. X. Liu, Z. Zhang, C. Han, et al., “Broadband long-wave infrared high-absorption of active materials through hybrid plasmonic resonance modes,” Discover Nano 18(1), 35 (2023). [CrossRef]
15. D. Hu, T. Meng, H. Wang, et al., “Ultra-narrow-band terahertz perfect metamaterial absorber for refractive index sensing application,” Results Phys. 19, 103567 (2020). [CrossRef]
16. J. Zheng, J. Zhu, Z. Yang, et al., “Extremely narrow resonant linewidths in metal-dielectric heterostructures,” Photonics Res. 10(7), 1754–1762 (2022). [CrossRef]
17. S. K. Verma and S. K. Srivastava, “Experimental demonstration of a Fano resonant hybrid plasmonic metasurface absorber for the O and E bands of the optical communication window,” J. Opt. Soc. Am. B 41(2), 356–363 (2024). [CrossRef]
18. B. Luk’yanchuk, N. Zheludev, S. Maier, et al., “The Fano resonance in plasmonic nanostructures and metamaterials,” Nat. Mater. 9(9), 707–715 (2010). [CrossRef]
19. B. Hopkins, A. N. Poddubny, A. E. Miroshnichenko, et al., “Revisiting the physics of Fano resonances for nanoparticle oligomers,” Phys. Rev. A 88(5), 053819 (2013). [CrossRef]
20. Y. Wen, W. Ma, J. Bailey, et al., “Planar broadband and high absorption metamaterial using single nested resonator at terahertz frequencies,” Opt. Lett. 39(6), 1589–1592 (2014). [CrossRef]
21. S. K. Verma and S. K. Srivastava, “Giant extra-ordinary near infrared transmission from seemingly opaque plasmonic metasurface: sensing applications,” Plasmonics 17(2), 653–663 (2022). [CrossRef]
22. S. K. Verma and S. K. Srivastava, “High performance extraordinary optical transmission based selfreferenced plasmonic metagrating sensor in the NIR communication band,” Phys. Scr. 98(5), 055515 (2023). [CrossRef]
23. T. Ebbesen, H. Lezec, H. Ghaemi, et al., “Extraordinary optical transmission through sub-wavelength hole arrays,” Nature 391(6668), 667–669 (1998). [CrossRef]
24. W. D. Li, J. Hu, and S. Y. Chou, “Extraordinary light transmission through opaque thin metal film with subwavelength holes blocked by metal disks,” Opt. Express 19(21), 21098–21108 (2011). [CrossRef]
25. U. Guler and R. Turan, “Effect of particle properties and light polarization on the plasmonic resonances in metallic nanoparticles,” Opt. Express 18(16), 17322–17338 (2010). [CrossRef]
26. A. T. M. Anishur Rahman, P. Majewski, and K. Vasilev, “Extraordinary optical transmission: coupling of the Wood–Rayleigh anomaly and the Fabry–Perot resonance,” Opt. Lett. 37(10), 1742–1744 (2012). [CrossRef]
27. A. López-Ortega, M. Zapata-Herrera, N. Maccaferri, et al., “Enhanced magnetic modulation of light polarization exploiting hybridization with multipolar dark plasmons in magnetoplasmonic nanocavities,” Light: Sci. Appl. 9(1), 49 (2020). [CrossRef]
28. M. Liu, W. Zhu, P. Huo, et al., “Multifunctional metasurfaces enabled by simultaneous and independent control of phase and amplitude for orthogonal polarization states,” Light: Sci. Appl. 10(1), 107 (2021). [CrossRef]
29. C. Huang, C. Zhang, J. Yang, et al., “Reconfigurable metasurface for multifunctional control of electromagnetic waves,” Adv. Opt. Mater. 5(22), 1700485 (2017). [CrossRef]
30. H. H. Hsiao, C. H. Chu, and D. P. Tsai, “Fundamentals and applications of metasurfaces,” Small Methods 1(4), 1600064 (2017). [CrossRef]
31. H. Zheng, Y. Zhou, C. F. Ugwu, et al., “Large-scale metasurfaces based on grayscale nanosphere lithography,” ACS Photonics 8(6), 1824–1831 (2021). [CrossRef]
32. V. Neder, Y. Radi, A. Alù, et al., “Combined metagratings for efficient broad-angle scattering metasurface,” ACS Photonics 6(4), 1010–1017 (2019). [CrossRef]
33. Y. Wang, Z. Cui, X. Zhang, et al., “Excitation of surface plasmon resonance on multiwalled carbon nanotube metasurfaces for pesticide sensors,” ACS Appl. Mater. Interfaces 12(46), 52082–52088 (2020). [CrossRef]
34. E. Ekmekci and G. T. Sayan, “Multi-functional metamaterial sensor based on a broad-side coupled SRR topology with a multi-layer substrate,” Appl. Phys. A 110(1), 189–197 (2013). [CrossRef]
35. S. Agarwal and Y. K. Prajapati, “Multifunctional metamaterial surface for absorbing and sensing applications,” Opt. Commun. 439, 304–307 (2019). [CrossRef]
36. X. Gao, Q. Ma, Z. Gu, et al., “Programmable surface plasmonic neural networks for microwave detection and processing,” Nat. Electron. 6(4), 319–328 (2023). [CrossRef]
37. L. Chen, Q. Ma, S. S. Luo, et al., “Touch-programmable metasurface for various electromagnetic manipulations and encryptions,” Small 18(45), 2270245 (2022). [CrossRef]
38. S. K. Patel, J. Surve, J. Parmar, et al., “Terahertz metasurface-based refractive index sensor for amino acid detection: a numerical approach,” IEEE Trans. NanoBiosci. 22(3), 814–821 (2022). [CrossRef]
39. S. Zhang, C. L. Wong, S. Zeng, et al., “Metasurfaces for biomedical applications: imaging and sensing from a nanophotonics perspective,” Nanophotonics 10(1), 259–293 (2020). [CrossRef]
40. J. Zheng, X. liu, M. Tian, et al., “Hybrid metal-dielectric gratings (HMDGs) as an alternative UV-SERS substrate,” Phys. Chem. Chem. Phys. 25(22), 15257–15262 (2023). [CrossRef]
41. B. I. Karawdeniya, A. M. Damry, K. Murugappan, et al., “Surface functionalization and texturing of optical metasurfaces for sensing applications,” Chem. Rev. 122(19), 14990–15030 (2022). [CrossRef]
42. X. Liu, R. Ma, and D. Sutherland, “A simple and high-performance platform for refractive index sensing based on plasmonic metal disks on a metal mirror,” IOP Conf. Ser.: Mater. Sci. Eng. 484(1), 012030 (2019). [CrossRef]
43. P. B. Johnson and R. W. Christy, “Optical constants of the noble metals,” Phys. Rev. B 6(12), 4370–4379 (1972). [CrossRef]
44. Z. Zhang, Y. Li, Z. Fu, et al., “Ethyl cellulose/rare earth complexes light-conversion films and exploration in acid rain detection,” Macromol. Mater. Eng. 307(1), 2100630 (2022). [CrossRef]
45. H. Li, J. T. Kim, J. S. Kim, et al., “Metasurface-incorporated optofluidic refractive index sensing for identification of liquid chemicals through vision intelligence,” ACS Photonics 10(3), 780–789 (2023). [CrossRef]
